A technique is proposed for the development of a real-time, 3- dimensional ultrasound-based visualization system for guidance of radioactive implants for treating prostate cancer. The system includes a real-time 3 dimensional imaging array and supporting 2D, 3D, and virtual reality visualization interfaces. Present techniques using transrectal ultrasound guidance for brachytherapy result in unacceptable rates of complication. The aim of the proposed technique is to reduce the complication rates and improve the local control rates by optimizing the visualization of seed implantation during ultrasound-guided brachytherapy. PROPOSED COMMERCIAL APPLICATION: The outcome of this research could be of immediate benefit in the treatment of prostate cancer using higher dose radiation with more accurate localization and fewer toxicities/less morbidity. It would provide the ability to "see through" the 3D prostate volume while placing implants A large group of patients with localized disease or who are poor surgical risks or who do not desire open surgery are candidates.